Bayer Leverkusen are reportedly demanding in excess of £90m to agree to the sale of Kai Havertz.
Having contributed 12 goals and six assists in the Bundesliga this season, Havertz is being heavily linked with a summer switch to Chelsea.
However, while it has been suggested that personal terms will not be an issue, the Blues are yet to agree a fee for the Germany international.
According to The Sun, Leverkusen want to receive £63m up front, with at least another £27m due in add-ons during Havertz's stay at Stamford Bridge.
The deal appears similar to the one which saw Eden Hazard leave Chelsea for Real Madrid, with the Premier League outfit recently receiving a return on one of their clauses due to Los Blancos winning La Liga.
Chelsea are said to be the only club willing to meet Leverkusen's valuation of their star man during the summer transfer window.
